Generally speaking, it is important to be able to determine the angular position of a rotor in order to optimize electrical performance in brushless DC motors in terms of improved efficiency, power factor, and reduced current. For this purpose, it has been possible to determine the angular position of a rotor absolutely, but not accurately, with certain techniques such as with an absolute sensor that measures the distance between the sensor and a rotating wheel where the distance is continuously variable. While such an absolute sensor can be utilized where temperature variations are negligible, and is well suited for use as a counter for determining the number of revolutions, it is not well-suited where accuracy is important in an atmosphere of power supply and temperature variations.
In the past, it has been proposed to determine the angular position of a rotor in an accurate but not absolute sense by utilizing a stationary magnetic sensor. For instance, this has been proposed in Rothley, U.S. Pat. No. 4,506,217 which also senses speed, and in Sato et al, U.S. Pat. No. 4,369,405 which utilizes rotating magnet poles in an AC power generated apparatus. Further, in Glauert et al, U.S. Pat. No. 4,166,977, a rotary speed and angular position determining system is disclosed.
Still other position and speed detecting apparatus are disclosed in U.S. Pat. Nos. 4,370,614; 4,490,674; 4,481,469; 4,506,339; 4,359,685; and 3,728,565. However, it has remained to provide a power and temperature independent magnetic position sensor for a rotor.
The present invention is directed to overcoming the above-stated problems and accomplishing the stated objects.